use std::io;

fn input_num() -> Vec<u64> {
    let mut s = String::new();
    io::stdin().read_line(&mut s).unwrap();
    let mut v = Vec::new();
    for i in s.split_whitespace() {
        v.push(i.parse().unwrap());
    }
    v
}

fn main() {
    let v = input_num();

    println!("{}", v[0] ^ v[1]);
}